It is particularly, but by no means exclusively, relevant to the flange-mounting of electric motors on off-the-shelf gear units. It is commonplace for the purchasers of such units to fit them with different sizes of motors to suit different gear ratios made available by fitting different gears in the same gear casing, and said motors frequently have different sizes of drive shafts. The input gear of such a unit is driveably connected to a steel sleeve mounted in bearings in the gear casing and having a bore with a conventional key-way of rectangular cross-section for the reception of the motor drive shaft. Where the motor drive shaft is nominally of the same diameter as the bore, they are driveably interconnected by a conventional steel key. Where, as frequently happens, the motor drive shaft is of smaller diameter than the bore, a slotted nylon sleeve is fitted to fill the annular space between them and they are driveably interconnected by a steel key of greater than normal height extending through the slot in said sleeve. Due to the fretting corrosion experienced between like metals in driving contact with one another, to the tendency of a key of greater than normal height to be tilted over by the torque transmitted through it, and to axial misalignment of the shaft and the sleeve due to the mounting flanges of the motor and the gear unit frequently being out of square with each other, failures of the key or of the bearing in the unit are not uncommon.
The object of the present invention is to avoid this problem.